1. Field of the Art
This invention relates to a method for forming a barrier metal structure within a minute contact hole opened in an insulation film layer on a substrate of a semi-conductor device or the like.
2. Description of the Prior Art
As a basic construction of semi-conductor devices, it has been known in the art to open a contact hole in a layer insulation film on a semi-conductor substrate of silicon or the like and to embed a wiring metal in the contact hole.
The construction of this sort has a number of problems which jeopardize the reliability of the semi-conductor device itself, for example, destruction of junction between a wiring aluminum layer and a silicon substrate by alloy pits formed due to the reaction between them, or an abrupt increase of contact resistance between the wiring layer and the substrate due to precipitation of silicon grains on the surfaces of the contact hole.
Therefore, for the purpose of improving the reliability of semi-conductor devices, it has become a widely accepted practice to deposit a barrier metal layer of TiN, TiW or the like within the contact hole, for example, by a spattering process, thereby preventing the undesirable reactions between the substrate material like Si and the wiring material like aluminum.
According to conventional design rules for semi-conductor devices, it has been possible to secure a sufficient coverage when forming a barrier metal layer or a wiring layer in a contact hole.
However, along with the recent developments of very large size integration devices, the design rules in this field of the art have reached a level of extreme fineness. This trend toward fine technology is also found in contact holes to be formed in insulation layers on semi-conductor substrates.
A fine contact hole of this sort involves a number of problems in connection with the coverage of a barrier metal layer or a wiring metal layer, especially in connection with the coverage in peripheral portions at the bottom of the contact hole. More specifically, as shown in FIG. 2, in order to prevent the reaction between a wiring layer of aluminum and a substrate of Si, it has been the general practice to deposit a layer of a barrier metal such as TiN, TiW or the like or of a silicide such as TiSi.sub.x in and over a contact hole 23 opened in an insulation film layer 22 on the Si substrate 21, before forming a wiring layer 25 of aluminum thereon. However, there are possibilities of the wiring metal itself breaking through the barrier metal layer 24 and getting into the Si substrate 21 to cause a junction leak when the coverage of the barrier metal layer 24 is poor, or of a void 26 being formed in the wiring layer when the coverage of the wiring metal itself is poor, degrading the reliability of the semi-conductor device to a considerable degree.